This disclosure relates in general to flowmeters and, but not by way of limitation, to multiphase flowmeters amongst other things.
Compared to in-line flowmeters, a clamp-on flowmeter offers strong operational and economical advantages. Some of these clamp-on flowmeters are designed to use ultrasound to monitor single-phase flows. However, these flowmeters may not be used to monitor multiphase flows that are common in the oil and gas industry.
For multiphase flows, some ultrasonic techniques are known to be capable of measuring the thickness of a liquid phase in a vessel or pipe. For example, by emitting a pulse signal and measuring an echo from a gas/liquid interface, a round-trip travel time of the pulse signal can be used to determine the gas/liquid interface position. However, a technique such as this requires a speed of sound in the liquid phase to be determined.
In order to determine the speed of sound in the liquid phase, various techniques generally require a length of the pulse signal's travel path to be known. However, in the oil-gas industry where the thickness of the liquid phase can vary from a few millimeters to a few centimeters, it is not practical to design a travel path such that a representative speed of sound can be determined from the travel path.